Stinging weed (6)
I believe the answer is:
nettle
'stinging weed' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for nettle that I've seen before include "Annoy - stinger" , "Annoy; common weed" , "Irritate, annoy" , "Upset" , "Stinging plant; annoy" .)